1. Field of the Invention
The present invention relates to a particle separation apparatus and method for separating particles in a suspension, with the specific gravities thereof or both the specific gravities and the particle diameters thereof as separation criteria.
2. Description of the Prior Art
Various particle separation apparatus using the specific gravities or particle diameters of two or more kinds of particles different in specific gravity as separation criteria and utilizing the difference in velocity of the underwater movements of the particles (jigs, tables, cyclones, etc. and their improvements) have heretofore been put to practical use at various places in the industrial fields.
The present inventors have already proposed a method for separating particles into large-gravity particles and small-gravity particles utilizing the difference in sedimentation velocity resulting from the difference in specific gravity of the particles, which method comprises giving a vibration in the direction in which the particles are settling down, utilizing the specific gravities of the particles and the frequencies and amplitudes of the vibration to make the sedimentation delay of the small-gravity particles larger than that of the large-gravity particles, thereby enlarging an equal settling ratio that is a particle diameter ratio of the particles different in specific gravity settling down at the same velocity (refer to JP-A 2003-340314).
In addition, a centrifugal separator having a structure in which a motor enables a partition wall to be rotated for solid-liquid-separating fine particles from a liquid has been known to the art (refer to JP-A SHO 63-62562).
Furthermore, the present inventors have already applied for a patent of the invention directed to means for separating fine particles every one group of particle diameters regardless of the difference in specific gravity, utilizing the application of centrifugal force under specific conditions (JP-A 2006-239678).
In a particle separation apparatus using the specific gravities or particle diameters of two or more kinds of particles different in specific gravity as separation criteria and utilizing the difference in velocity of the underwater movements of the particles, since the velocity of movement of the particles in water depends on both the specific gravities and the particle diameters (projected cross-sectional areas) of the particles, there are cases where particles of large gravity and small particle diameter and particles of small gravity and large particle diameter move at the same velocity and where particles of small gravity moves at a higher velocity than particles of large gravity.
In order to separate particles into groups different in specific gravity with high accuracy, therefore, it is required to remove in advance particles large particle diameter and small gravity higher in velocity than particles of large gravity and particles of small particle diameter and large gravity lower in velocity than particles of small gravity.
Since it is impossible to beforehand remove particles having specific particle diameters into groups different in specific gravity, it is generally adopted to use a method capable of separating with a sieve the particles according to the particle diameters regardless of the specific gravities to obtain particles adjusted to a specific particle size width range. While preparatory particle size adjustments to the range of approximately several millimeters to several centimeters are ready to make, it is very difficult to industrially adjust particles having particle diameters smaller than 50 to 100 μm to specific particle size widths.
Major conventional fine particle separation apparatus have been provided with a system applying a centrifugal field to increase the particle movement velocity. However, since the centrifugal force, as well as the gravitational force, is a force depending on both the specific gravities and the particle diameters of the particles, it has few effects on spreading of the particle size width to be preparatorily adjusted, as shown in FIG. 3(a), while it enables the time required for separation to be shortened.
With the prior art techniques, therefore, it has been impossible to separate fine particles, particularly, polydisperse fine particles with high precision according to specific gravities (or particle diameters). Means available to date for separating such polydisperse fine particles according to specific gravities with high precision utilizing the difference in underwater movement thereof include (1) a one-stage process comprising controlling the particle movement at the time of separation by the specific gravity to separate the fine particles according to the specific gravities with high precision regardless of the particle diameters or reducing the degree of particle-diameter dependency of the fine particles to be separated to enlarge the particle size width to be preparatorily adjusted, thereby actually dispensing with the preparatory particle size adjustment and (2) a two-stage process comprising establishing a technique capable of separating, according to the particle diameters with high precision regardless of the specific gravities, fine particles preparatorily adjustable to the particle size required for the separation according to the specific gravities and then performing an existing method of separation according to the specific gravities.
JP-A 2003-340314 cited above relates to a method comprising affording a specific vertical vibration to water to control the movement of particles in water, thereby enlarging the particle size width to be adjusted preparatorily. Thus, it corresponds to one-stage process (i) above and, since it has its limits on a variable particle size width, it is difficult to completely dispense with the particle size adjustment.
JP-A 2006-239678 cited above relates to a technique corresponding to two-stage process (2) above with the aim of solving the aforementioned conventional problem, and resorting to means for affording a centrifugal force under specific conditions to enable separation of the particles according to their particle diameters irrespective of the difference in specific gravity.
An object of the present invention is to provide a technique that further improves the technique disclosed in JP-A 2006-239678 and realizes a technique corresponding to two-stage process (2) above, in which a centrifugal force is given under specific conditions different from those used in JP-A 2006-239678 to thereby enable separation of fine particles according to their specific gravities or to both their particle diameters and their specific gravities.